The products of this invention are materials containing distinct, interpenetrating polymer and liquid phases of submicroscopic, but supramolecular, dimensions. Such products are referred to as a polymer-liquid composite (PLC).
A PLC material can serve as media for diffusive and permeative phenomena commonly associated with pure liquids, while displaying the physical form and integrity of solids, and is useful for controlling the release or exchange of liquids and solutes, while their finite internal pore size allows processing and partitioning of liquids and solutes on the basis of molecular size and shape. Further, a PLC can be used in many applications where some known liquid possesses desirable chemical, electrical or other properties, but lacks the required mechanical integrity. These useful properties often are enhanced at high liquid-to-solid ratios. The present invention presents a unique, novel and general category of high liquid content PLC material which, unlike familiar high liquid content polymer gels, retains good mechanical properties.
The PLC materials of this invention are distinct from the plasticized polymers of commerce, such as polyvinylchloride/dioctyl phthalate and polymeric gels, such as gelatin or cross-linked polyacrylamide. Plasticized polymers, even when their liquid content reaches or exceeds 50%, can be considered rather accurately as solutions of a liquid in a solid. The physical properties of plasticized polymers can be and generally are profoundly modified by the presence of the liquid; tensile strength and elastic moduli are reduced, and softening points or transition temperatures fall to lower values than those for the pure resin, and such changes are often of crucial commercial importance. Such common plasticized polymers are categorized as rather soft and elastic solids. Liquid transport through such materials, even at high pressure gradients, is too slow to be useful for membrane separation processes and the rapid diffusion characteristic of the free molecular motion found in pure liquids is not exhibited by plasticized polymers. The dispersion of the polymer and liquid phases in plasticized resins is essentially molecular, and encounters between moving fluids or individual molecules and the immobile polymer molecules are extremely frequent, leading to virtual immobilization of the entire system.
At much higher liquid concentrations, I find the common polymer gels, which may show some nonamorphous morphology, particularly when based on proteins or polysaccharides with their stereospecific biological origin and strong hydrogen-bonding ability. Nevertheless, the degree of dispersion of the polymer and liquid in each other is still generally molecular, with the solid or semisolid characteristics of the gel arising from entanglement or weak bonding between the long, intermingled polymer chains. Synthetic gel-forming polymers, such as polyacrylamide, are often cross-linked to impede further relative motion and enhance physical integrity. Fluid and diffusive mobilities within such gels can be high when there is very little polymer present, but this low polymer concentration and the lack of any pronounced morphological reinforcement between neighboring molecules leads to very low physical strength, often defeating the very application for which the gel would otherwise be suited. For example, one gains little through preparing a gel which would give rapid liquid flux rates through a thin film at some given pressure gradient, if the gel itself collapses under the applied pressure.
These two classes of materials, plasticized polymer and polymer-liquid gels, have in common the feature that, although composed of two distinguishable substances, one a liquid and the other a solid, on any scale of much more than molecular dimensions, they present all of the characteristics of a single phase material, and are not considered to be true composites. Just as some metals alloy randomly in all proportions, while others precipitate as separate phases to produce materials such as steel or alnico with a whole new set of properties, so liquids and polymers can in some cases function merely as mutual solvents and solutes, or alternatively separate into distinct interpenetrating phases and develop characteristics found in neither alone. It is this latter category which is termed polymer-liquid composites (PLC), and which comprises the materials of the invention.